There is a conventionally-known spectral measurement apparatus configured to irradiate a sample as a measurement object with excitation light and detect light to be measured, and as a technology of this kind, for example, Patent Document 1 describes the quantum efficiency measurement apparatus. The quantum efficiency measurement apparatus described in this Patent Document 1 is configured to integrate reflection components from a fluorescent substance of single-wavelength radiation and all radiation components of excited fluorescence emission by an integrating sphere to measure a spectral energy distribution thereof, and to integrate all reflection components from a spectral reflectance standard of single-wavelength radiation by the integrating sphere to measure a spectral distribution thereof. Then the apparatus calculates the number of photons absorbed by the fluorescent substance and the number of photons of the fluorescence emission, based on the measurement values, and calculates a quantum yield of the fluorescent substance from a ratio of these numbers.
Furthermore, for example, Patent Document 2 describes the absolute fluorescence quantum efficiency measurement apparatus configured as follows; in obtaining a quantum yield, the sample is fixed at a position where the sample is not directly hit by the excitation light in the integrating sphere, and the absorptance of the sample is obtained from an intensity obtained with indirect incidence of the excitation light to the sample and an intensity obtained with direct incidence of the excitation light to the sample. Non Patent Documents 1 to 3 describe calculation of quantum yields on the premise that the excitation light is made incident to a part of the sample.